Sustainable Approaches for 1D Supercapacitors and Triboelectric Devices based on Functionalized Carbon Fiber Yarns

Carbon fibers (CFs) are versatile materials for energy harvesting and storage applications, particularly when focusing on wearable device applications. They present a combination of some unique properties, such as suitable electrical conductivity and mechanical strength, being also lightweight.<br/>Stretch-broken carbon fiber yarns (SBCFYs) can be used as current collectors to fabricate 1D fiber-shaped supercapacitors (FSCs) using regenerated cellulose-based electrolyte. The areal-specific capacitance reaches 433.02 µF cm^-2 at 5 µA cm^-2. The maximum achieved specific power density is 0.5 mW cm^-2, at 1 mA cm^-2. The 1D FSCs possess a long-life cycle, 92% capacitance retention after 10000 charge/discharge cycles. The specific capacitance can be improved through functionalization of CFs with MoS₂ nanosheets, reaching 58.6 F g^-1 at 1 mV s^-1 with a power density of 15.17 W g^-1 and energy density of 0.5 mWh g^-1.<br/>Functionalization of CF by introducing functional groups or nanoparticles onto the fiber surface is also crucial in optimizing power conversion efficiency in energy harvesting devices, such as triboelectric ones. We propose triboelectric generator yarns (TEG yarns) with axially grown ZnO nanorods using a new method for depositing PDMS directly onto conductive carbon yarns. The in-situ PDMS curing method allows the fast formation of a uniformly thick coating over functionalized CFs. Single-electrode configuration TEG yarns were developed, and their electrical output was optimized by precisely adjusting the PDMS layer thickness and by changing the chemical and physical nature of the SBCFYs surface, reaching a power density of 74.1 μW cm^-2. We demonstrate that electrodeposited cellulose nanocrystals layers can replace ZnO nanorods in improving local polarization, which results in an increase of 100% of the TEGs electrical output to around 142.7 μW cm^-2.<br/>Both SBCFYs supercapacitors and triboelectric devices can be hand-stitched onto fabrics showcasing the practicality and versatility of the prepared 1D CFs energy harvesting and storage devices to power the future generation of wearables electronics.